Engines may be configured with various fuel systems used to deliver a desired amount of fuel to an engine for combustion. Port fuel direct injection (PFDI) engines include both port injection and direct injection of fuel and may advantageously utilize each injection mode. For example, at higher engine loads, fuel may be injected into the engine using direct fuel injection for increased engine performance (e.g., by increasing available torque and fuel economy). At lower engine loads and during engine starting, fuel may be injected into the engine using port fuel injection to provide increased fuel vaporization for enhanced mixing and to reduce engine emissions. Further, port fuel injection may provide increased fuel economy over direct injection at lower engine loads. In addition, both port injectors and direct injectors may be operated together under some conditions to leverage advantages of both types of fuel delivery or, in some instances, differing fuels.
In PFDI engines, a lift pump (also termed, low pressure pump) supplies fuel from a fuel tank to both port fuel injectors and a direct injection fuel pump (also termed, high pressure pump). The direct injection fuel pump may supply fuel at a higher, variable pressure to direct injectors. In some examples, the port fuel injection (PFI) portion of the PFDI system may be mechanically controlled to a fixed PFI fuel rail pressure via an in-tank regulator. In other examples, the PFI system may be controlled via closed-loop pressure control. Operating at the fixed PFI fuel rail pressure may increase lift pump usage, which increases electrical power consumption, while operating with closed-loop pressure control requires feedback from a PFI fuel rail pressure sensor, which increases system costs. Therefore, vehicle manufacturers may weigh the cost of including a PFI fuel rail pressure sensor against savings in electrical power consumption when choosing the control strategy of the PFI portion of the PFDI system.
Furthermore, some engines may be configured to operate with a variable number of active or deactivated cylinders to increase fuel economy, known as variable displacement engines (VDE). Therein, a subset of the cylinders may be disabled during selected conditions defined by parameters such as a speed/load window while remaining cylinders continue to produce torque. A VDE control system may disable the subset of cylinders, such as a bank of cylinders, through the control of a plurality of cylinder valve deactivators that affect operation of the cylinder's intake and exhaust valves and through deactivating fuel injectors of the subset of cylinders. Further increases in fuel economy can be achieved in engines configured to vary the effective displacement of the engine by skipping the delivery of fuel to certain cylinders in an indexed cylinder firing pattern, also referred to as a “skip-fire” pattern. Such engines may be referred to as rolling variable displacement engines (rVDE).
The inventors herein have recognized that when a PFDI system is combined with rVDE technology, the PFI system is rarely used. For example, instead of using PFI for increased fuel economy at lower engine loads, the engine may instead operate with a subset of the cylinders deactivated, with fuel directly injected in the remaining active cylinders. Because the PFI system is rarely used, how it is controlled has a relatively small impact on electrical power consumption.
In one example, the issues described above may be addressed by a method for fueling an engine, comprising: selecting between operating a lift pump in a pressure relief mode and a variable pressure mode based on whether the engine is fueled via port fuel injectors; and adjusting an output of the lift pump while operating in the variable pressure mode based on a fractional volume loss of a high pressure pump measured while operating the lift pump in the pressure relief mode. In this way, the lift pump may be controlled in a higher electrical power consumption mode (e.g., the pressure relief mode) only while PFI is performed, and operation in the pressure relief mode may be opportunistically used for high pressure pump fractional volume loss calibration for subsequent operation in a lower electrical consumption mode (e.g., the variable pressure mode).
As one example, operating the lift pump in the pressure relief mode includes supplying fuel at a fixed lift pump outlet pressure, the fixed lift pump outlet pressure defined by a pressure setpoint of a mechanical pressure relief valve positioned downstream of the lift pump with no additional pressure relief valves positioned in between. Furthermore, operating the lift pump in the pressure relief mode includes supplying voltage to the lift pump that is greater than or equal to a threshold voltage. As another example, operating the lift pump in the variable pressure mode includes supplying fuel at a variable lift pump outlet pressure that is less than the fixed lift pump outlet pressure, such as by supplying voltage to the lift pump that is less than the threshold voltage. While operating the lift pump in the variable pressure mode, the variable lift pump outlet pressure is adjusted based on the fractional volume loss of the high pressure pump measured while operating the lift pump and further based on a current fractional volume loss error value of the high pressure pump so that the high pressure pump is operated at a desired volumetric efficiency. The pressure relief mode is selected when the engine is fueled at least partially via the port fuel injectors, and the variable pressure mode is selected when the engine is fueled via the direct injectors only. Notably, port fuel injection may be performed during limited conditions, such as engine start and at high (e.g., higher than a threshold) engine speeds. Instead of using port fuel injection, the engine may be transitioned into a variable displacement engine mode at low (e.g., lower than a threshold) engine loads. As such, the pressure relief mode may be rarely selected during engine operation.
While the high pressure pump may be controlled at least partially based on feedback from a pressure sensor at a direct injection fuel rail, the lift pump is controlled without feedback from a pressure sensor. Due to operating the lift pump in the pressure relief mode when port fuel injection is performed, a pressure at a port fuel injection fuel rail is inferred as a fixed, mechanically regulated pressure. In this way, lift pump operation during port fuel injection, direct injection, or both may be accurately controlled without feedback from a pressure sensor, and port fuel injection may also be accurately controlled without feedback from a pressure sensor. As a result of omitting a pressure sensor for lift pump and port fuel injection control, fuel system costs are reduced. As a result of omitting the pressure sensor in the fuel system of a rVDE, additional lift pump power consumption due to operating in the pressure relief mode is reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.